Develop a better dermal index for discriminating dermal microsymptoms in high risk Down's syndrome parents. Reanalyze correlation of quantitative dermal index with percentage of plus 21 cell in 46/47, plus 21 mosaics. Accumulate and code larger 0% plus 21 and 100% plus 21 groups to accomplish goals 1) and 2). Analyze the differences in dermal pattern assignment by different investigators and develop ways to overcome this problem. Continue analysis of more plus 21 Down's syndrome families to discriminate origin of the nondisjunction and correlate with parental clinical and/or dermal microsymptoms. Improvement of chromosome 21 polymorphism analysis by development of a computer program to study densitometric strip chart recorder tracings of Q-banded photographic negatives. Plan and implement a protocol for a cooperative study of mosaic evolution in young 46/47, plus 21 mosaics.